Abstract: The thermodynamics of basic oxide-aluminate and borate systems are approached in terms of statistical polymer theory. Alinear chain model is presented for binary aluminate systems, in which the ion AlO₃^3- and BO₃^3- are treated as the monomeric unit. The activities of the constituents can be expressed as functions of the Al₂O₃ and B₂O₃ content under the assumption that the systems exhibit Temkin behavior and do not produce ring anions. The activities predicted for several systems are in agreement with experimental values. Quantitative expression of free energy of mixing is derived. Gel point is related to the limitation of application of polymer theory to the melts.